It is known that many aquatic invertebrates such as crustaceans go through a cycle of molting, in which an old hard shell is shed and a new larger soft shell is grown. Depending on the stage of the molting process, the crustacean's internal body, i.e., the “meat” portion of the lobster, may occupy a reduced part of the internal volume of the new shell as the internal body grows to occupy the new, larger shell. The internal structure of the crustacean, including its organs, meat and muscle, is undersized in proportion to its new shell after molting. In order to “fill out” this new, oversized shell, the crustacean takes on and retains water within its internal structure. As a result, inter-molt crustaceans (hard shell) generally produce high meat yields, while post-molt (soft shell) crustaceans generally produce very low meat yields.
Seafood is often an expensive food product for which a consumer pays a premium. In return, the consumer expects to receive a high quality product that reflects the price paid. For example, consumers will often pay a premium for larger crustaceans, in terms of weight and/or size, and the consumer will generally expect the size of the crustacean to correspond to the amount of meat yielded by the crustacean. However, due to the variance in the ratio of intracellular water to extracellular water in the shell cavity of the crustacean, i.e., the ratio of the amount of water stored in the muscle or “meat” of the crustacean to the amount of water stored outside of the muscle to “fill out” the shell, a larger post-molt crustacean may not yield any more meat than a smaller pre-molt or inter-molt crustacean.
Inter-molt crustaceans can often be identified by their hard shells and other external characteristics such as color. However, these measures are unreliable as a means to determine meat yields and are difficult to implement as non-invasive measures on a production line. Other attempts at sensing systems employing ultrasound or x-ray scanning systems have proven difficult to implement and failed to accurately distinguish between different shell hardnesses and/or different meat yields.
Beyond meatedness, the molt state of a crustacean can also be used as a “health” indicator that provides a seafood processor with the advantage of being able to assess anticipated mortality rates during storage.
Conventional meat yield sensing systems have relied on an assumed correlation between the refractive index (RI) of the blood of crustaceans and the stage of molt of a crustacean, and hence the meatedness of the lobster. However, while these methods may be fairly accurate at predicting meat yield, they require an invasive blood test of the crustacean and the use of a refractometer to determine the RI of the blood, which is impractical in a production plant setting at typical production rates.
In addition, conventional means of detecting meatedness are difficult to assess on live seafood product, at production speeds, because of varying pose/position of the crustacean under test.